The present disclosure relates generally to power supplies that provide a constant DC output current to a load, such as, for example, light-emitting diodes. More particularly, the present disclosure relates to a lighting device including output buffer circuitry to stabilize operation in a standby mode or a no-load mode.
The usage of light-emitting diodes (LEDs) to provide illumination is increasing rapidly as the cost of LEDs decrease and the endurance of the LEDs increases to cause the overall effective cost of operating LED lighting products to be lower than incandescent lamps and fluorescent lamps providing equivalent illumination. Also, LEDs can be dimmed by controlling the current through the LEDs because LEDs are current driven devices. The current through a plurality of LEDs in a lighting device must be controlled tightly in order to control the illumination provided by the LEDs. Typically, the secondary (output side) of an LED lighting device must be electrically isolated from the primary (line and neutral side) of the lighting device to meet applicable safety standards (e.g., IEC class II isolation). In addition, an LED driver circuit should desirably have a high power factor and constant voltage control.
For standard operating conditions, an exemplary lighting device according to various conventional designs will operate in a continuous mode and serve as a constant voltage supply to a load connected thereto. However, during non-standard operating conditions, such as a no-load condition or a low power standby condition, conventional lighting devices may be configured to operate in a pulse mode so as to maintain the desired average output voltage. This may be undesirable for a number of reasons, particularly in one exemplary context as described herein where an auxiliary circuit is provided to receive input power from the active driving circuit and further serve as a power supply for the control circuitry.
In applications where for example a dimming controller is provided as part of a feedback circuit to receive and process external dimming input signals, it would be desirable for such circuitry to remain effective during all operating modes for the lighting device.